Use this API :
Windows.System.Launcher.LaunchUriAsync(new System.Uri("URI_below"));
tubecast:
tubecast:VideoID=zSJUMAExTI4
tubecast:ChanneID=UCvUyrJmBljmpj3yH4a7o-iA
tubecast:PlaylistID=PLbl2SbVIi-Wrpnd2sZTvo_Jkb1Fy-P0z-
If you prefers open in "an official way" every youtube app that handle the official vnd.youtube Schema, Tubecast handle it too !
vnd.youtube:zSJUMAExTI4
You can also open Tubecast through a YouTube URL (URLEncode it before) like this :
tubecast:link=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DzSJUMAExTI4